The processing of analog input parameters, such as temperature or pressure, is particularly widely common in the processing industry. Many of these signals serve for process monitoring and thus they are frequently of decisive relevance for the safety of the process.
Unlike digital signals, the analog technology is rather expensive, though. The easiest way to check analog circuits for their function is comprised of applying a reference source to the analog circuit, for example, and comparing the value measured with the target value.
However, particularly the requirements of the safety standard DIN EN 91508 for the diagnostics coverage of higher security integrity levels (e.g., SIL2 or SIL3) at the time of the present application are still possible only with an enormously expensive circuitry.
In particular, in order to meet such higher safety integrity standards, other redundantly embodied signal processing structures and respective diagnostics scenarios are known in prior art, to be mentioned here are for example DE 10 2007 062 974 of the same applicant, DE 2 108 496 A, EP 1 643 323 A1, US 2005/240806 A1, U.S. Pat. No. 5,838,899, U.S. Pat. No. 4,358,823, US 2002/0152420 A1, US 2006/0010352 A1, U.S. Pat. No. 6,985,975, EP 2 175 371, EP 2 207 097, EP 2 228 723, EP 2 196 908, U.S. Pat. No. 7,949,833, U.S. Pat. No. 7,979,746, or U.S. Pat. No. 8,037,364.